The invention relates, in general to a device for regulating the output of a single or multi-stage compressor arrangement, particularly screw-type compressors of the type having a throttle valve at the suction end and a blowoff valve at the discharge or pressure end, and as well as a regulator controlling the operation of the valves which can be subjected to a control pressure through a measuring pipe connected to the pressure pipe of the compressor arrangement carrying the end pressure, and which, when the end pressure rises to within a control range, before switching to no-load operation, control the partial closing of the throttle valve to regulate the output, with the blowoff valve closed.
Such a regulating device is disclosed in West German Offenlegungsschrift No. 27 37 677, which corresponds to U.S. patent, now U.S. Pat. No. 4,212,599, the disclosures of which is incorporated herein by reference. The known device effects the regulation of the output, which adapts itself to varying amounts tapped, and works substantially without energy loss due to unnecessary blowoff. This is achieved by providing that the blowoff valve can be closed only after a leading closing angle of the throttle valve has been closed. Thus, a control range of the throttle valve is available, before this closing angle is reached, in which the output can be regulated by partially closing the throttle valve with the blowoff valve closed.
The control characteristic of the known device, however, is not optimal, since a closing operation, once it has started, is ended only when the throttling at the suction end also manifests itself in the end or discharge pressure. During transient fluctuations of the end pressure, the throttle valve can, therefore, be overdriven, that is, closed unnecessarily wide, so that fluctuations of the throttle valve, and even unnecessary opening movements of the blowoff valve can result.
West German Offenlegungsschrift Nos. 16 48 501 and 14 28 065 teach the tapping of control pressure from the suction and discharge ends for controlling adjusting elements for a throttle valve at the suction end and a blowoff or blowdown valve at the pressure or discharge end.